Method and device for cylindrical grinding

ABSTRACT

A method for cylindrical grinding of cylindrical workpieces on a grinding machine, in which an axes of rotation of a grinding disc and of the workpiece are aligned in parallel to one another and the grinding disc is moved relative to the workpiece in a longitudinal-axial direction of the workpiece during the grinding process. A first grinding disc is followed by a second grinding disc at a continuously constant distance. The distance is determined by the width of the first grinding disc and the remaining grinding parameters, such as the rotational speeds of the first grinding disc and of the workpiece and the feed rate in the longitudinal-axial direction, such that the second grinding disc grinds the helical error lines generated by the first grinding disc during the grind process. A control device adjusts the distance between the first and second grinding discs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a United States National Phase Application of International Application PCT/DE2021/100596, filed Jul. 8, 2021, and claims the benefit of priority under 35 U.S.C. § 119 of German Application 10 2020 120 617.8, filed Aug. 5, 2020, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a method for cylindrical grinding of cylindrical workpieces on a grinding machine, in which the axes of rotation of a grinding wheel and the workpiece are aligned parallel to one another and the grinding wheel is moved during grinding relative to the workpiece in the longitudinal axial direction of the workpiece.

TECHNICAL BACKGROUND

Grinding is suitable for manufacturing parts with tightly toleranced dimensions that cannot be produced by turning or milling. The advantages of grinding are, in particular, good machinability of hard materials, high dimensional and shape accuracy as well as small waviness and roughness.

The rotating grinding wheels have grinding grains whose position in the grinding wheel is undefined for each grain, so that grinding is referred to as cutting with geometrically undefined cutting edges. With external cylindrical longitudinal grinding, the workpiece is guided along the grinding wheel via the longitudinal feed of a workpiece slide. Another variant is the so-called centerless cylindrical grinding, in which the round, cylindrical workpieces are pressed against the grinding wheel by a control wheel when being processed with a grinding wheel.

Regardless of which external cylindrical grinding method is selected, the grinding wheels used for longitudinal grinding often leave a helical fault line on the workpiece, which depends on the feed.

SUMMARY

It is an object of the present invention to specify a method and a grinding device with which such surface defects on the workpiece surface are eliminated or at least minimized to small roughness depths.

This object is achieved by a method according to the invention, characterized in that a second grinding wheel follows the first grinding wheel at a constant distance, the distance being determined by the width of the first grinding wheel and the other grinding parameters such as the rotational speeds of the first grinding wheel and of the workpiece and the feed in the longitudinal axial direction is determined in such a way that the second grinding wheel grinds the helical fault lines which the first grinding wheel has produced during grinding.

In other words, in the method according to the invention, a second grinding wheel eliminates the surface defects in the workpiece that occur in a helical form. The shape, arrangement or drive of the second grinding wheel can be selected optional, as long as it is ensured that the aforementioned helical boundary line on the workpiece surface is reworked.

The grinding wheels can have abrasive grains with the same or different granulometry.

Preferred configurations result from the disclosure.

According to a preferred embodiment, the first and second grinding wheels are mounted on the same axis of rotation and are driven at the same rotational speed during grinding. This has the advantage that only one drive needs to be used.

Surface defects can also be optimally avoided if both grinding wheels are subjected to the same contact pressure during grinding.

In principle, the grinding method according to the invention can be used for counter-rotating or co-rotating grinding wheels and workpieces, a co-rotating grinding wheel and workpiece provided that different rotational speeds are selected so that a relative movement between the grinding wheel and the workpiece can be set.

To solve this problem, the grinding device described in claim 5 is used, which is characterized by a second grinding wheel, the distance to the first grinding wheel is rotatably arranged. Both grinding wheels preferably have a common variable or controllable drive and/or are arranged on the same axis.

In order to be able to select different grinding speeds, which have a decisive influence on the helical shape of the fault line, the distance between the first grinding wheel and the second grinding wheel can be adjusted. Ideally, a control device is provided that adjusts the distance between the first and second grinding wheel in such a way that the second grinding wheel sweeps over the helical fault lines during grinding, which the first grinding wheel previously produced. With this control device, an optimized surface treatment can be ensured even with small fluctuations in the longitudinal feed.

Further advantages and features of the device according to the invention and the method according to the invention are shown in the drawings.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 a, FIG. 1 b and FIG. 1 c are schematic views of the external cylindrical longitudinal grinding methods known according to the state of the art and the resulting grinding faults; and

FIG. 2 shows a schematic perspective view of the grinding device according to the invention with a first and second grinding wheel.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings, From FIG. 1 a it can be seen that on the cylindrical workpiece, the surface of which is to be ground by grinding, helical fault lines can occur during external cylindrical longitudinal grinding, which can occur, for example, due to non-parallel guidance of the surface line of the grinding wheel to the longitudinal slide movement or thermal influences or wear of the abrasion tool (for the grinding wheel). The grinding wheel 12 leaves such helical grinding marks whose gradient is determined by the feed of the grinding wheel relative to the workpiece 10 represented by the arrow 13. The cylindrical workpiece 10 rests on rollers 14, 15, which are preferably equally spaced serve as support and drive rollers for the rotary movement of the workpiece.

FIG. 1 b and 1 c show different drive options:

According to the method according to FIG. 1 b, the drive rollers 14, 15 on which the cylindrical workpiece rests are rotated in the opposite direction to the direction of rotation of the grinding wheel 12. The grinding wheel 12 and the cylindrical workpiece 10 move in the same direction of rotation, which is why the rotational speeds of the cylindrical workpiece 10 and the grinding wheel must be different for grinding.

In the process technology according to FIG. 1 c, the drive rollers 14, 15 drive the workpiece in a direction which is opposite to the direction of rotation of the grinding wheel 12.

As shown in FIG. 2 , in the grinding method according to the invention, in addition to the first grinding wheel 12, a second grinding wheel 16 is used, which in the present case has the same diameter as the first grinding wheel 12 and which is mounted on the same axis of rotation. The grinding wheels 12 and 16 have the same rotational speed due to a common drive (not shown). The distance between the first grinding wheel 12 and the second grinding wheel 16, which can be variably adjusted via a control device (not shown), depends on the spiral or helical course of the surface defects on the workpiece 10. The second grinding wheel follows this helical line of defects and eliminates the surface defects.

In principle, the method according to the invention is suitable for all external cylindrical or internal cylindrical grinding processes, regardless of the dimensions of the workpiece and the material of which the workpiece is made.

As a side effect, post-processing of the workpiece surface can also be achieved in the simplest way with the method according to the invention. The first and the second grinding wheel can be fixed so that the workpiece feed is generated by a linear movement of the cylindrical workpiece 10. As an alternative to this, when the workpiece is firmly clamped, the tandem grinding wheel pair consisting of the first and second grinding wheel can also be moved longitudinally and axially to the workpiece.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

REFERENCE CHARACTER LIST

-   10 cylindrical workpiece -   11 helical boundary lines -   12 grinding wheel -   13 feed direction -   14, 15 drive rollers -   16 second grinding wheel 

1. A method for cylindrical grinding of cylindrical workpieces on a grinding machine, the method comprising the steps of: aligning axes of rotation of a first grinding wheel and a workpiece parallel to one another; moving the first grinding wheel relative to the workpiece during grinding in a longitudinal axial direction of the workpiece; providing a second grinding wheel that follows the first grinding wheel at an always constant distance, the distance being determined by a width of the first grinding wheel and other grinding parameters comprising rotational speeds of the first grinding wheel and of the workpiece; and determining a [[the]] feed of the second grinding wheel in the longitudinal axial direction such that the second grinding wheel grinds the helical fault lines that the first grinding wheel has produced during grinding.
 2. A method according to claim 1, wherein the first and the second grinding wheel (12,) are mounted on a same axis of rotation and are driven at a same rotational speed during grinding.
 3. A method according to claim 1, wherein both grinding wheels are applied to a same contact pressure during grinding.
 4. A method according to claim 1, wherein the grinding wheels on the one hand and the workpiece on the other hand are rotated in opposite directions or in a same direction, but at different rotational speeds.
 5. A grinding device comprising: a first grinding wheel configured to be driven to rotate about an axis of rotation which runs parallel to the longitudinal axis of a workpiece to be machined; a feed device which causes a relative movement between the workpiece and the grinding wheel in the longitudinal axial direction of the workpiece; a second grinding wheel arranged rotatably at a distance from the first grinding wheel; and a control device configured to adjust a distance between the first and the second grinding wheel in such a way that the second grinding wheel sweeps over a helical fault line that the first grinding wheel previously produced.
 6. A grinding device according to claim 5, wherein both grinding wheels are arranged on a same axis and have a common variable or controllable drive.
 7. A grinding device according to claim 5, wherein the distance between the first grinding wheel and the second grinding wheel can be adjusted.
 8. A method according to claim 2, wherein both grinding wheels are applied to a same contact pressure during grinding.
 9. A method according to claim 8, wherein: the grinding wheels are rotated in one direction and the workpiece is rotated in a direction opposite to the one direction; or the grinding wheels are rotated in one direction and the workpiece is rotated in a same direction top the one direction but at a different rotational speed.
 10. A method according to claim 2, wherein: the grinding wheels are rotated in one direction and the workpiece is rotated in a direction opposite to the one direction; or the grinding wheels are rotated in one direction and the workpiece is rotated in a same direction top the one direction but at a different rotational speed. 